1. Field of the Invention
The present invention relates in general to sampling and pressure-volume-temperature (PVT) analysis of hydrocarbon samples using two-dimensional gas chromatography (GC×GC).
2. Background of the Invention
The petroleum industry uses a variety of chemicals while drilling wells for the recovery of hydrocarbons from geologic reservoirs. Synthetic-based muds (SBM) and conventional (diesel/mineral) oil-based muds (OBM) as drilling fluids are becoming increasingly common because of the rapid drilling rates and increased hole stability associated with their use. This mud filtrate is usually present as a contaminant at some level in the collected hydrocarbon samples and alters the physical properties and phase behavior of the reservoir fluid samples. The level of contamination determines the extent to which the measured fluid properties will vary from actual. Collecting representative samples of hydrocarbons in an oil field for laboratory analysis for pressure-volume-temperature (PVT) labs is essential for determining gas-oil ratios, phase transition pressures, viscosities, composition and various other parameters, which is useful for building production facilities and for developing production strategies. Therefore, it is essential for laboratories to quantify the level of mud filtrate contamination very accurately in collected samples to understand and compensate for the effects of the contamination on the fluid properties of the original reservoir fluid.
The most common technique for quantifying contamination due to SBM/OBM filtrate is based on traditional one-dimensional gas chromatography with flame ionization detection (GC−FID), using “skimming” and “subtraction” methods. These methods are expensive in terms of number of analysis to be done. Moreover, one-dimensional gas chromatography usually has oil peaks which overlap with contamination peaks making determination difficult. In addition, one-dimensional gas chromatography can suffer at low levels of contamination where it is obscured by more dominant petroleum hydrocarbons, which may lead to low sensitivity as well as poor accuracy. Thus, one-dimensional gas chromatography of a typical contaminated crude oil does not provide sufficient resolution to determine unambiguously the amount of contamination. Thus, there remains a need in the art for new methods for accurately estimating contamination due to SBM/OBM filtrate in crude oil samples.